The present invention relates to disk drives and, in particular, to the writing of servo tracks on a disk within the disk drive.
A disk drive is a device that is commonly employed in computer systems to store data. Typically, a disk drive includes: (1) one or more disks that each have a plurality of concentric tracks on which data is stored; (2) a spin motor for rotating the disk or disks; (3) one or more heads that are each capable of writing and/or reading data to/from a track on a disk; (4) an actuator for moving the head or heads to a desired location adjacent to a disk so that data can be written to the disk or read from the disk; and (5) circuitry for transferring data between a disk and a portion of a host computer system that is exterior to the disk drive, such as a random access memory (RAM).
A disk drive also typically includes a servo system that operates to move a head over a defined track on a disk surface and maintain the head over the defined track until directed to move the head over a different track. The servo system maintains the position of the head over a defined track based upon information that is read from a servo track. In one type of drive, the servo tracks are embedded in or coincident with the user data tracks, i.e., the servo track and the user data track form a single physical track with the servo data interspersed among the user data. Typically, the servo track: (1) identifies the particular track over which a head is positioned; and (2) provides data from which the position of the head relative to the center line of the track can be determined. The identification of the particular track is primarily used when the head is being moved from one track to another track (which is commonly known as a seek operation) to determine when the head is positioned over the desired track. Once the head is over the desired track, data indicating the position of the head relative to the center line of the track is determined and used to maintain the head over the desired track (which is commonly known as a tracking operation). For example, if the data indicates that the head is positioned to one side of the center line, the servo system causes the actuator to move the head towards the center line.
Presently, the servo tracks are usually written on the disk surfaces of a disk drive during the manufacturing process by a servo track writer. Further, the operation is usually done in a clean room environment to prevent contamination of the disk drive. As a consequence, the throughput of a manufacturing facility is limited by the number of servo track writers that are available and the availability of clean room space to house the servo track writers.
As an alternative to using a servo track writer, the drive itself can be used to write the servo tracks in what is known as self servo writing operation. In this case, a motor associated with the actuator is used to move the actuator arm in discrete steps to write each servo track.
The present invention is directed to a disk drive that uses a multi-stage actuator to write servo tracks on the disks. The multi-stage actuator includes a primary actuator for coarsely positioning a head and a secondary actuator for finely positioning the head.
In one embodiment, a disk drive includes at least two separate and substantially parallel disk surfaces that are capable of storing data. Associated with each disk surface is a head for transferring data between the disk surface and the exterior environment. A multi-stage actuator is used to move the heads to desired positions over the disk surfaces for the transfer of data. The multi-stage actuator includes a primary actuator for coarsely positioning the heads relative to the disk surfaces. Associated with each head is a secondary actuator that permits the position of the head to be more finely controlled. The data transfer circuitry of the disk drive, which is normally used to write/read user data to/from the disk, is also adapted to write the servo tracks on the disk surfaces. To elaborate, a servo system associated with the data transfer causes the primary and secondary actuators associated with the first head to position the first head for writing the initial servo track on the first disk surface. After the initial servo track has been written on the first surface, the initial servo track is used as a reference relative to which the secondary actuator associated with the second head positions the second head to write the initial servo track and possibly several servo tracks on the second disk surface. A servo track on the second disk surface is subsequently used as a reference relative to which the secondary actuator associated with the first head positions the head to write one or more servo tracks on the first disk surface. This process of alternatingly using a servo track on one disk surface as a reference relative to which the secondary actuator associated with the head over another disk surface positions the head to write servo tracks is repeated until, for a given position of the primary actuator, substantially all of the servo tracks have been written. The primary actuator is then repositioned and the process is repeated until all of the servo tracks have been written on the disk.
In another embodiment, the primary actuator is positioned with respect to a known physical reference point before the initial servo track is written on the first disk surface. One such physical reference point is a crash stop that is used to prevent the primary actuator from moving the heads beyond a predetermined range. By using such a physical reference point, any positional error in the initial servo track is substantially reduced. As a consequence, a potential source of positional error in the subsequently written servo tracks is substantially eliminated.
In yet a further embodiment, the primary actuator is positioned to substantially reduce the number of times that the primary actuator must be repositioned in order to write all of the servo tracks on the first and second disk surfaces. To elaborate, at least with respect to certain bands of servo tracks, the primary actuator is positioned so that the secondary actuators are able to traverse substantially their entire range of motion during the writing of the servo tracks. As a consequence, as many servo tracks as possible are written before the primary actuator is repositioned.